Conventional turbine nozzle guide vanes have to withstand high levels of stress in the aerofoil and in particular in the trailing edge fillets. This stress is mostly caused by different heating and cooling rates within the components during transient operations conditions of the turbine. Aerofoils of the guide vanes are formed on an inner platform that extends in a circumferential direction of the turbine shaft. From the inner platform, the aerofoils extend radially outwardly. From the inner platform in radial direction to the center of the turbine shaft an inner rail is attached. The inner rail is used to mount a diaphragm between the surface of the turbine shaft and the inner platform. The inner rail is in general thicker and broader than the inner platform to which the inner rail is attached, so that the inner rail reacts slower in response to temperature changes in the turbine with respect to the inner platform. This may result in thermally induced stress and reduces the lifetime of the conventional nozzle guide vane devices.
In conventional turbine nozzle guide vanes, the stresses may be reduced by keeping the depth and width of the inner rail to a minimum required. This may also lead to a reduction of the lifetime of the inner rail respectively to the turbine nozzle guide vane and reduces the quality of fixation of the diaphragms.
U.S. Pat. No. 4,126,405 describes a segment of a turbo machine nozzle that is held tangentially in position by a pair of lugs extending radially from outer and inner bands. Each lug acts as an end cap to prevent leakage of air from one end of the vane.
EP 1 793 088 A2 discloses a turbine nozzle for a gas turbine engine. The turbine nozzle comprises an outer band and an inner band. Between the inner band and the outer band vanes are formed. To the inner band a flange and a forward inner flange is formed, wherein the flanges extend radially inwardly from the inner band.
U.S. Pat. No. 3,829,233 discloses a seal arrangement for a bladed diaphragm of an axial flow fluid machine, such as a gas turbine. The turbine comprises an inner shroud from which the vanes extend radially outwardly with respect to the turbine shaft and from which flanges and ribs extend radially inwardly. To the flanges and ribs a seal housing ring or a diaphragm is attached, so that the inner shroud is sealed from the turbine shaft. The inner shroud comprises an orifice for cooling fluid, wherein the orifice is spatially located from the flanges and ribs.